Optical system for smartphone cameras enhancing ZOOM capabilities and enabling long-distance macro photograph

Abstract

The invention consists of a device to be applied to smartphone cameras in order to enhance their zoom capabilities and to enable long-distance macro photography. The device comprises an add-on lens specifically designed to be applied to smartphone cameras having equivalent focal lengths greater than 30 mm. The invention makes it possible to obtain a 2× magnification factor with minimal distortion while preserving excellent image quality. In addition, the invention provides a set of additional accessories configured to shorten the minimum focusing distance of the optical system and to allow long-distance macro photograph.

Description

[0001] OPTICAL SYSTEM FOR SMARTPHONE CAMERAS ENHANCING ZOOM CAPABILITIES AND ENABLING LONG-DISTANCE MACRO PHOTOGRAPH

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a device to be applied to smartphone cameras in order to enhance their zoom capabilities and to enable long-distance macro photograph.

[0004] BACKGROUND OF THE INVENTION

[0005] In recent years, advances in lens systems and sensors for smartphones have led to a significant improvement in the photographic and video capabilities of mobile devices. The adoption of aspherical lenses, high-resolution CMOS sensors, and sophisticated imageprocessing techniques has made smartphones competitive with professional cameras (reflex or mirrorless).

[0006] As is well known, a smartphone camera comprises a lens, characterized by its effective focal length, and a sensor for converting light into electronic signals useful for forming the image.

[0007] The first smartphone models were equipped with a single fixed-focal-length camera, which did not allow the user to access optical zoom (the only available zoom being digital, implemented by software). In more recent models, an increasing number of manufacturers have integrated multiple cameras into the same smartphone, having different focal lengths and sensors. By way of example, the iPhone 15 ProMax is provided with three distinct cameras: a 24 mm wide-angle, a 13 mm ultra- wide-angle, and a 120 mm telephoto. The above focal lengths are to be considered as equivalent focal length (i.e., 35mm equivalent focal length).

[0008] Despite recent progress, smartphone cameras still present the following limitations:

[0009] 1) The limited thickness (a few millimeters) of a smartphone imposes strict constraints on the geometry of the optical system. The limited thickness also imposes restrictions on the dimensions of the sensor.

[0010] 2) The reduced size of the sensor limits the size of the pixels forming it. Smaller pixels collect less light and are more sensitive to noise (thermal or electrical).

[0011] 3) The lenses of smartphone cameras are fixed and non-interchangeable. This limits the user to a discrete number of focal lengths and fixed fields of view.

[0012] There is therefore a need to expand the photographic capabilities of smartphone cameras. For this purpose, various add-on lenses have been introduced, to be applied in front of the integrated cameras in order to modify their focal length. Such add-on lenses behave like teleside converters, already known in the market of reflex or mirrorless cameras. The add-on lenses currently available on the market are designed to convert the wide-angle lenses of smartphones into ultra-wide-angle, telephoto, fisheye, macro, and anamorphic lenses.

[0013] It should be emphasized that these add-on lenses are designed to be applied to wide- angle cameras, with focal lengths shorter than 30 mm. Consequently, when applied to integrated telephoto cameras, a significant loss of optical performance is observed, resulting in low image quality.

[0014] SUMMARY OF THE INVENTION

[0015] The subject matter of the present patent is a new add-on lens specifically designed to be applied to smartphone cameras having equivalent focal lengths greater than 30 mm. With an appropriate combination of optical elements, the invention makes it possible to achieve a 2- magnification factor, with minimal distortion while preserving excellent image quality. When applied to the telephoto camera of an iPhone 15 ProMax, the invention converts the equivalent focal length from 120 mm to 240 mm. Accordingly, with respect to the 24 mm wide-angle camera, an optical magnification of 10x is obtained.

[0016] The subject matter of the present patent according to claim 1 is a lens system for smartphone camera, comprising a plurality of elements arranged along the optical axis of the lens system, wherein the plurality of elements includes, in order along the optical axis from the object side to the image side: i. a first element being an optical doublet having a positive lens on the object side and a negative lens on the image side; ii. a second element being a single lens having a concave surface on the object side and a convex surface on the image side; iii. a third element being a single lens having a concave surface on the object side and a concave surface on the image side; and wherein the lens system provides a 2* magnification when applied to a smartphone camera having an equivalent focal length equal to or greater than 30 m.

[0017] Further features are provided in the dependent claims and concern: a lens system in which the first and second elements have a positive focal length while the third element has a negative focal length; a lens system that satisfies one or more of the following relationship: a. 0,8 < fl / f2 < 1,6 b. -2,9 < fl / fi < -3,9 c. 2,1 < f2 / f3 < -3,0 where fl is the focal length of the first element (doublet), f2 is the focal length of the second element, and f3 is the focal length of the third element; a lens system in which the first element is a doublet made of two optical materials having a refractive index in the range of 1.5 < nd < 1.9 and an Abbe number in the range of 20 < Vd < 65; a lens system in which the second and third elements are made of optical materials having a refractive index in the range of 1.7 < nd < 1.9 and an Abbe number in the range of 20 < Vd < 60; a lens element to be applied to the lens system, located between the object side and the first element of the lens system; a lens element having an effective focal length in the range of 50-500 mm configured to decrease the minimum focusing distance of the lens system as described above to a value in the range of 50-500 mm; a lens element that is an achromatic doublet having a positive refractive power; a support body containing the lens system, encasing an array of permanent magnets on the object-side surface to allow the magnetic attachment of optical or mechanical accessories; a support body containing the above-mentioned lens element, having a ferromagnetic ring facing the image side to be attached to the support body; a telephoto lens comprising a central body containing the above-described lens system and, at the base of said central body, a mount configured for installation on said smartphone camera having equivalent focal lengths greater than 30 mm; a telephoto / macro accessory system comprising a telephoto lens as described above and a macro accessory having a focal length of 200 mm configured to be applied to said telephoto lens.

[0018] LIST OF FIGURES

[0019] Further features and advantages will become more apparent from the following exemplary, but non-limiting, description of preferred embodiments of the present invention, illustrated with the aid of the accompanying drawings, in which:

[0020] - Figure 1 illustrates, in exploded view, the device according to the invention;

[0021] - Figure 2 illustrates the structure of the invention;

[0022] - Figure 3 shows a summary table of the parameters of Figure 2;

[0023] - Figure 4 illustrates the optical structure of a possible macro accessory;

[0024] - Figure 5 shows a summary table of the parameters of Figure 4; - Figure 6 illustrates the device of Figure 1;

[0025] - Figure 7 illustrates, in exploded view, an accessory applicable to the device of Figure 1;

[0026] - Figure 8 illustrates the accessory of Figure 7 applied to the device of Figure 1;

[0027] - Figure 9 illustrates the device in complete assembly;

[0028] - Figure 10 shows the Optical Transfer Function graph of the device of Figure 1;

[0029] - Figure 11 shows the spot diagram of the device of Figure 1;

[0030] - Figure 12 shows the Optical Transfer Function graph of the device of Figure 1 with macro.

[0031] DETAILED DESCRIPTION OF THE INVENTION

[0032] The optical structure of the invention, in one preferred but non-limiting embodiment, is shown in Figure 2. The telephoto lens comprises an optical doublet LI (Figure 2, items 11-10) and two single lenses, L2 and L3 (Figure 2, items 6-8). The geometry of each optical element is defined by the radius of curvature of the optical surfaces and by the thickness dimension. The position of the optical elements is defined by the distances reported in the table of Figure 3. The reported distances or thicknesses refer to the distance between the vertices of the optical surfaces (vertex-to-vertex distance), where the vertex of an optical surface is defined as the point on the optical axis at which the surface intersects the axis itself. The optical axis, passing through the center of each lens, is represented by the horizontal line in Figure 2

[0033] The distance d3 in Figure 2 may vary from a minimum of 27 mm to a maximum of 30 mm and determines the minimum focusing distance of the optical system. Each optical element is further characterized by a specific optical material, having a given refractive index nd and Abbe number Vd, as reported in the table of Figure 3. Finally, each optical element is characterized by a mechanical semidiameter (or radius), which defines its final dimensions while taking into account an appropriate tolerance for housing the elements within the lens body (Figure 1). The effectiveness of the invention as described above is demonstrated by the Optical Transfer Function graph (Figure 10) and the spot diagram (Figure 11).

[0034] In its original form, described in one preferred but non-limiting embodiment in Figure 2, the invention allows optical magnification (10x with respect to the wide-angle camera of an iPhone 15 ProMax) of objects located at distances greater than 5-7 m from the lens. However, it is also possible to exploit the above magnification factor for nearby objects, thereby converting the invention into a macro lens.

[0035] As is well known, a macro lens is a photographic lens specifically designed for closeup photography, allowing images to be obtained with a high degree of magnification. Generally, a macro lens has the capability of reproducing a subject at a 1 : 1 scale (life size) on the sensor. Add-on lenses for smartphones defined as macro lenses are designed to operate on the wide- angle camera (for example, the 24 mm camera on the iPhone 15 ProMax). These lenses function to shorten the minimum focusing distance of native wide-angle cameras, allowing the focusing of objects very close to the lens (2-7 mm from the lens). However, this approach presents the following disadvantages:

[0036] 1) The wide-angle camera does not provide sufficient optical magnification.

[0037] 2) To obtain magnifications typical of macro photography, it is necessary to shoot at only a few centimeters from the subject.

[0038] 3) The short distance does not allow convenient photographing of insects or small animals, as these tend to flee at the sight of the lens.

[0039] 4) The short distance casts a shadow on the subject, creating problems with light and exposure.

[0040] There is therefore a need to obtain magnifications typical of macro photography at greater object-to-lens distances. The invention of this patent allows long-distance macro photography through the application of converter accessories, which reduce the minimum focusing distance (from 5-7 m to 50-500 mm). Thanks to the aforementioned 10x optical magnification, it is possible to obtain magnifications typical of macro photography at much greater distances than those offered by currently available solutions.

[0041] The optical structure of a possible macro accessory Ml, in one preferred but nonlimiting embodiment, is shown in Figure 4, items 14-15. The optical design of the macro converter accessory is therefore composed of two lenses (Figure 4, items 14-15) forming a doublet. This doublet configuration ensures the correction of possible chromatic aberrations. The radii of curvature, thicknesses, mechanical semidiameter, and materials of element Ml are reported in the table of Figure 5. The position of doublet Ml with respect to the first element LI of the add-on lens of this patent may vary from 1 to 5 mm. The macro accessory Ml is placed in front of element LI of the lens, on the object side.

[0042] In this example, the macro accessory has a focal length of 200 mm and ensures that the minimum focusing distance of the telephoto / macro accessory system is 200 mm. This makes it possible to take macro photographs at a distance of 200 mm from the subject. The optical performance of the 2* lens shown in Figure 2 with macro accessory Ml (Figure 4) is demonstrated by the Optical Transfer Function (OTF) reported in Figure 12.

[0043] The structure of the invention, in one preferred but non-limiting embodiment, is shown in Figure 1, which illustrates the exploded view of the device, composed as follows: a central body (Figure 1, item 1) containing the optical design consisting of a combination of lenses (Figure 1, items 6-8-10-11); at the base of the body (Figure 1, item 1) there is the mount of the invention (Figure 1, item 4) for installation on the smartphone camera to which it is intended.

[0044] At the top of the lens body there is a fixing ring of the optical system (Figure 1, item 3), to which magnets are attached (Figure 1, item 5). A closing ring is provided (Figure 1, item 2) to cover the magnets; finally, a cover cap for the entire invention is present (Figure 6, item 12).

[0045] Inside the body (Figure 1, item 1) there are lenses (Figure 1, items 6-8) held in place by the centering and fixing ring (Figure 1, items 7-9); in the upper part, two lenses (Figure 1, items 10-11) are fixed together to form the upper doublet.

[0046] As stated above, the device, as described and shown in one preferred but non-limiting embodiment, can be equipped with accessories that enable long-distance macro photography (Figure 6). The macro accessories are applied, when needed, on top of the closing ring (Figure 1, item 2); these accessories consist of a separate lens system called a macro converter and illustrated in exploded view in Figure 7. The macro converter comprises a central body (Figure 7, item 13) which contains two lenses (Figure 7, items 14-15) fixed at the base by the lower shell of the macro converter accessory (Figure 7, item 16). The two lenses (Figure 7, items 14- 15) form a doublet. In Figure 8, the device consisting of the 2* telephoto lens with the application of the macro converter accessory is shown, the body of which remains visible (Figure 9, item 13).

[0047] The complete assembly of the elements described above is shown in Figure 9, where it is possible to view: the central body containing the 2* telephoto lenses (Figure 9, item 1), the mount of the 2* telephoto lens for installation on the intended device (Figure 9, item 4), and the body of the macro converter accessory (Figure 9, item 13).

[0048] The device thus conceived and described is susceptible to modifications and variations, all of which fall within the scope of the inventive concept, and all details may be replaced with technically equivalent elements. Furthermore, the contingent dimensions and shapes may be of any kind according to requirements and the state of the art

Claims

CLAIMS1. A lens system for a smartphone camera, comprising: a plurality of elements arranged along the optical axis of the lens system, wherein the plurality of elements includes, in order along the optical axis from the object side to the image side: i. a first element being an optical doublet having a positive lens on the object side and a negative lens on the image side; ii. a second element being a single lens having a concave surface on the object side and a convex surface on the image side; iii. a third element being a single lens having a concave surface on the object side and a concave surface on the image side; wherein the lens system provides a 2* magnification when applied to a smartphone camera having a 35 mm equivalent focal length equal to or greater than 30 mm.

2. The lens system as recited in claim 1, wherein the first and second elements have a positive focal length, and the third element has a negative focal length.

3. The lens system as recited in claim 1, wherein the lens system satisfies one or more of the following relationship: a. 0,8 < fl / f2 < 1,6 b. -2,9 < fl / fi < -3,9 c. 2,1 < f2 / f3 < -3,0 where fl is the focal length of the first element (doublet), f2 is the focal length of the second element, and f3 is the focal length of the third element.

4. The lens system as recited in claim 1, wherein the first element is a doublet made of two optical materials having a refractive index in the range of 1.5 < nd < 1.9 and an Abbe number in the range of 20 < Vd < 65.

5. The lens system as recited in claim 1, wherein the second and third elements are made of optical materials having a refractive index in the range of 1.7 < nd < 1.9 and an Abbe number in the range of 20 < Vd < 60.

6. A lens element to be applied to the lens system as recited in claim 1, located between the object side and the first element of the lens system.

7. The lens element as recited in claim 6, having an effective focal length in the range of SO- SOO mm configured to reduce the minimum focusing distance of the lens system as recited in claim 1 to a value in the range of 50-500 mm.

8. The lens element as recited in claim 6, being an achromatic doublet having a positive refractive power.

9. A support body containing the lens system as recited in claim 1, encasing an array of permanent magnets on the object-side surface to allow the magnetic attachment of optical or mechanical accessories.

10. A support body containing the lens element as recited in claim 6, having a ferromagnetic ring facing the image side to be attached to the support body as recited in claim 9.

11. A telephoto lens comprising a central body (1) containing the lens system as recited in claim 1 and, at the base of said central body (1), a mount (4) configured for installation on said smartphone camera having equivalent focal lengths greater than 30 mm.

12. A telephoto / macro accessory system comprising a telephoto lens as recited in claim 11 and a macro accessory (Ml) having a focal length of 200 mm configured to be applied to said telephoto lens.

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